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July 15, 2011 -- A new study affirms that the 2009 H1N1flu vaccine, developed to counter the flu pandemic, does not substantially put people at increased risk of Guillain-Barré syndrome. Guillain-Barré syndrome is a disorder in which a person's immune system damages nerves, causing weakness and in some cases paralysis.

The study, conducted at five centers throughout Europe, was published in the latest issue of BMJ.

The concern about Guillain-Barré dates back 35 years. That’s when a vaccine with an added substance called an adjuvant, which stimulates the immune system, appeared to make users of the vaccine seven times more likely to develop the disease. That vaccine, developed by the United States, was withdrawn. Although adjuvanted vaccines developed after 1976 have shown no similarly heightened risk, concern about their safety has remained high.

“Even though the studies repeatedly showed risk estimates well below the sevenfold increase of 1976, they do not provide reassurance that there is no increase in risk after seasonal influenza vaccination,” the authors write.

Guillain-Barré, a rare disorder that affects one to two people out of 100,000, has no known cause. However, about half of all cases occur after a viral or bacterial infection. Weakness and tingling in the legs are early symptoms of the disease. In severe cases, the disorder causes total paralysis and unassisted breathing becomes impossible. Recovery can take from a few weeks to a few years, and a small number of people with the disorder will experience a relapse.

GBS and Swine Flu Vaccine

For the study, researchers in Denmark, France, the Netherlands, Sweden, and the U.K. combed through the health records of approximately 50 million people for the period between November 2009 and March 2010. They were looking for cases of Guillain-Barré syndrome and a variant of the disorder known as Miller-Fisher syndrome. They found 154.

After adjusting for various factors, the study team concluded that there were three cases of Guillain-Barré syndrome for every 1 million people vaccinated with adjuvanted vaccines. In 1976, there had been one case per 100,000 people who were vaccinated.

“Our point estimate shows no association between pandemic influenza vaccination and Guillain-Barré syndrome,” the authors conclude. “The consistent pattern across countries provides reassurance about the findings.”

An accompanying editorial from vaccine experts at the CDC says the results of this study are similar to those in studies on non-adjuvanted vaccines conducted in the United States and China. No adjuvanted vaccines are used in the U.S., the authors write.

“Nonetheless,” the authors of the editorial conclude, “the safety findings on adjuvanted flu vaccines will be important if such vaccines become more common in the future, whether in seasonal flu vaccines or for the next pandemic.”